It is desirable to scan the contents of objects such as, for example bottles or other containers, at security and customs checkpoints to gain information about content based on radiation received at a detector after interaction with the object and obtain an indication that the contents of the object do not constitute a threat to security or a breach of customs regulations. It is also desirable to scan the contents of objects for other purposes such as quality control, content verification, degradation monitoring etc.
To ensure that the contents of an object are consistent throughout the object, or that an object does not contain hidden compartments, or components, or to ensure that the contents are what they are claimed to be, it may be useful to scan the object and contents so that a high energy ionising radiation beam traverses a cross section of the object. It can be possible to obtain an indication of the materials composition from a numerical analysis of the resultant transmitted radiation beam intensity data.
A preferred means of scanning the contents of an object is to cause the object to move relative to the high energy radiation beam and detector. For scanning relatively small objects, such as bottles that might be carried through an airport security checkpoint, for ease of operation it is desirable to move the bottle rather than the bulky and heavy radiation source and detector assembly. In either case, a relative linear movement of object through scanning zone effects a scan along a selected path through the object, for example under the action of suitable drive means.
It has been found that when the transmitted beam of high-energy ionising radiation is detected at a suitable detector after it has passed through the object and its contents, during a scan along a selected cross section of the object, the electric motor typically used to power a drive means driving the movement of the object relative to the radiation source and detector may cause electromagnetic signals that may interfere with the signal representative of the radiation detected at the detector, making it more difficult to analyse the signals to accurately identify the materials present in the object. There is also a compromise to be considered between the desire for fast throughput of objects (which tends to favour a high scanning rate) and the requirement, for effective materials identification, of a sufficiently high count rate through a given object feature. For both these and for other reasons the effectiveness of materials identification by numerical analysis of the transmitted radiation beam intensity might be diminished.
There is a need for an improved method, system and apparatus for undertaking scanning of objects and/or their contents using high energy ionising radiation, where a transmission radiation beam is measured by a detector and the radiation beam source and detector move relative to the object such that a cross section of the object can be scanned. There is a particular need for security applications for a high throughput rate method of scanning objects comprising containers of contained materials which by their nature will be expected to have a single generally homogeneous composition.